Forage testing is used to estimate the nutritional value of forage for livestock rations. It involves sampling and lab analysis. The information gained is most useful if it is correctly used in the development and feeding of balanced rations, or in some cases in hay marketing.

The first and most important step in obtaining a meaningful analysis is to collect a representative forage sample. This fact sheet outlines methods for collecting and preparing hay and silage samples for analyses. It also provides a description of and sources for sampling tools.

1. Sample by forage lot

A forage lot is that hay or silage taken from the same location, field or farm, the same cutting (within a 48-hour period) at the same plant maturity and having similar amounts of grass, weeds, rain damage or preservative treatment. A lot may also be several bales to several tons of purchased hay.

Do not be tempted to save money and combine hays of different qualities or cuttings into one composite sample; the resulting analysis information will not be useful for making feeding decisions. Keep a record of quantity and location of each lot sampled.

2. When to sample

This is impractical when marketing hay ‘out of the field,’ for lots moving through ‘marketing channels’ and where individual lots of hay have limited accessibility.

For silage, some producers sample and test the forage as it is going into storage, but it is still best to sample and test nearer the time of feed out. Allow enough time for mailing, laboratory work, and ration formulation. This may require several days to a week or more in total.

3. Samples must be representative of the feeds being fed – use a core sampler

Use a core sampler or ‘hay probe’ to collect the forage sample from bales or stacks after harvest. A core sampler is a sharpened tube that collects an accurate representation of the actual proportions of leaves and stems as they exist in the bale.

A core sampler should have an inside diameter of 3⁄8 to 1 inch. An extremely small diameter coring device may not cut or represent the leaf-stem ratio properly, and a very large diameter probe may obtain too large a sample, which is difficult for labs to grind properly.

The sampler tube length should be 12 to 24 inches. Longer probes (greater than 24 inches) have the disadvantage that very large samples are generated, which in itself is not a problem, but analysis errors may come from labs sub-sampling from a very large submitted sample.

A sharp cutting tip improves the efficiency of sampling and helps to collect a more representative sample. Re-sharpen cutting tips regularly.

Core samplers may be available for loan from extension specialists, nutrition consultants or other producers. While the cost of owning your own core sampler may seem high, it is generally very economical compared to the costs of livestock production losses from incorrect rations or the feeding of unneeded supplements.

4. Sampling bales and stacks of hay

Sample large round bales by taking cores (also 12 to 15 inches deep) at waist height on the rounded, tight side. If only a few large square or round bales make up the lot, take multiple cores from each bale to equal 20 cores. Sample stacks and chopped hay 18 inches deep.

Avoid sampling spoiled or weathered portions of bales or stacks that will not be fed. If using a hand brace or low-powered portable electric drill, you may be tempted to collect fewer than 20 cores. Sampling error and inadequate representation of the lot variability increases if fewer than 20 cores are collected.

Consider using an electric corded drill powered by a portable generator if bale storage is in a remote location.

The 20 core samples from the lot should be about one pint to two quarts in volume, or about half a pound of material, and will represent several tons of forage.

Mix the collected hay cores in a clean, plastic pail. Place the entire sample (a combination of all 20 core samples) into a clean, heavyweight plastic bag. Seal the bag tightly to maintain sample moisture.

5. Sampling chopped silage crops and baleage

For large fields harvested over several days, collect two to four handfuls of chopped forage from each of several loads during each day. Combine all the samples from the field in a sealed plastic bag and submit this large, composite sample to the laboratory, frozen.

A more accurate representation of the quality of forage being fed is from silage samples taken after fermentation, at feed-out. Collect grab samples at both morning and evening feeding when feeding a new silage lot. Avoid sampling spoiled silage from the top of the bunker or at the transition between lots in an upright or bunker silo.

When sampling from the face of a bunker silo or from a plastic silage bag, mechanically remove the forage as it will be fed and collect grab samples from that volume. Freeze these grab samples.

The accumulated grab samples (several quarts weighing two to three pounds) should be thoroughly mixed, sealed in a plastic bag and frozen for shipment or delivery to the testing lab.

For many, it seems more practical to sample during silo filling. While there are some nutritional changes during normal fermentation, nutritional changes are usually small.

However, if forage is stored ‘too wet’ and the silo ‘seeps’ or it is stored ‘too dry’ and the silage heats excessively during ensiling, consider re-sampling by taking several grab samples at feed out, to account for nutritional changes during ensiling.

Baled wet or wilted forage being stored as bale silage can be done either by core sampling bales before wrapping for bale silage, or sampling the wrapped bales nearer the time of feeding. If sampled plastic-wrapped bales are not being fed immediately, reseal quickly to prevent unnecessary spoilage.

6. Keep good records

This lot identification should match your record of where the lots are located. It is also a good practice to write a brief description of the type of forage included in the sample: for example, ‘alfalfa hay,’ ‘mixed clover (70 percent) orchardgrass (30 percent) hay,’ ‘rye silage,’ etc.

Some laboratories use this information in the analysis procedures. Keep a record of similar information for your own future reference, as well as information about rain or insect damage, preservative used, etc. that would be useful to you or the livestock producer when interpreting the analysis.

7. Ship samples immediately